The Kinematics of Cluster Galaxies via Velocity Dispersion Profiles

TL;DR

This study analyzes the velocity dispersion profiles of 14 galaxy clusters to understand how merging activity influences galaxy kinematics and accretion modes within clusters.

Contribution

It provides the first detailed comparison of kinematic profiles between merging and non-merging galaxy clusters using SDSS and X-Ray data.

Findings

Merging clusters show active kinematic mixing with infalling substructures.

Non-merging clusters exhibit declining kinematic activity with radius.

Blue galaxies tend to have higher velocities, indicating fast infall.

Abstract

We present an analysis of the kinematics of a sample of 14 galaxy clusters via velocity dispersion profiles (VDPs), compiled using cluster parameters defined within the X-Ray Galaxy Clusters Database (BAX) cross-matched with data from the Sloan Digital Sky Survey (SDSS). We determine the presence of substructure in the clusters from the sample as a proxy for recent core mergers, resulting in 4 merging and 10 non-merging clusters to allow for comparison between their respective dynamical states. We create VDPs for our samples and divide them by mass, colour and morphology to assess how their kinematics respond to the environment. To improve the signal-to-noise ratio our galaxy clusters are normalised and co-added to a projected cluster radius at $0.0 - 2.5$ $r_{200}$. We find merging cluster environments possess an abundance of a kinematically-active (rising VDP) mix of red and blue elliptical galaxies, which is indicative of infalling substructures responsible for pre-processing galaxies. Comparatively, in non-merging cluster environments galaxies generally decline in kinematic activity as a function of increasing radius, with bluer galaxies possessing the highest velocities, likely as a result of fast infalling field galaxies. However, the variance in kinematic activity between blue and red cluster galaxies across merging and non-merging cluster environments suggests galaxies exhibit differing modes of galaxy accretion onto a cluster potential as a function of the presence of a core merger.